1. Field of the Invention
The present invention relates to a method of manufacturing a positive electrode for a lithium ion secondary battery.
2. Description of Related Art
Japanese Patent Application Publication No. 2009-064770 (JP 2009-064770 A) discloses a method of manufacturing a nonaqueous electrolyte secondary battery, in which a heat treatment is performed on a positive electrode current collector foil and a positive electrode mixture after the positive electrode mixture is applied to the positive electrode current collector foil and dried.
In JP 2009-064770 A, the current collector foil is softened in order to improve safety in a crushing test. Specifically, the heat treatment is performed to soften the current collector foil after the positive electrode mixture is applied to the current collector foil and dried to form a positive electrode mixture layer. However, according to this method, the positive electrode mixture layer and the current collector foil undergo the heat treatment at the same temperature. As a result, a binder contained in the positive electrode mixture layer is melted, and resistance increases.
The reason why the soft current collector foil is not used from the beginning is that it is difficult to accurately form the positive electrode mixture layer on the soft current collector foil that is easy to deform.